Conventional golf balls can be divided into two general types or groups: solid balls or wound balls. The difference in play characteristics resulting from these different constructions can be quite significant. These balls, however, have primarily two functional components that make them work. These components are the center or core and the cover. The primary purpose of the core is to be the “engine” of the ball or the principal source of resiliency. The primary purpose of the cover is to protect the core.
Two-piece solid balls are made with a single-solid core, usually made of a crosslinked polybutadiene or rubber, which is encased by a cover material. These balls are typically the least expensive to manufacture as the number of components is low and these components can be formed by relatively quick, automated molding techniques. In these balls, the solid core is the “engine” or source of resiliency. The resiliency of the core can be increased by increasing the crosslink density of the core material. As the resiliency increases, however, the compression also increases making a harder ball, which is undesirable.
Polybutadiene cores in solid balls are adversely affected by moisture, and to protect against moisture their covers should have good moisture barrier properties and should be applied to the cores soon after their formation. One way to achieve a desirable golf ball is to cover a high-velocity polybutadiene core with a urethane cover. This type of golf ball exhibits low driver spin and high velocity for distance with high half-wedge spin for control around the greens. Since urethane lacks optimal moisture barrier properties, a polybutadiene core of such a two-piece ball, however, can lose its high velocity quickly, which is undesirable. As a result, balls with polybutadiene cores and urethane covers may include an intermediate layer for moisture control.
High velocity cores have also been covered with blends of low modulus ionomers, which offer better moisture barrier properties than urethane. These covers, however, lack resiliency so that the desired ball velocity is not achieved.
Hence, there remains a need for a two-piece ball design that provides a soft, high-velocity core and a surrounding soft cover layer for low driver spin with high velocity and high half-wedge spin while also having good moisture barrier characteristics.